If you do go for a gill net (the wise choice) you may be wondering about it's set-up, you can of course just take a sheet of net and codge it up when needed with bouyancy like empty containers and weights like stones and the like, however a properly made-up net will be much better and easier to use and more efficient, you can use ''float-line'' for the top which is just cord with inserted bouyancy at intervals (this an alternative to normal floats and packs away neatly, though normal floats are fine but they must be bigger than mesh size to stop falling through meshes and becoming tangled), and for weight you can use ''lead-line'' attached to the bottom (just cord with string of beads of lead weights inserted inside cord), leadline is much better than individual weights as it eliminates any tangles, it comes in different weights and you need only the lightest which is not much heavier than the cord itself, the correct setting up is ratio of float versus weight so you can design it to be a surface fisher or bottom fisher, surface i feel is better for your needs, for super efficiency stick to monofilament, it's the best material, don't make the mistake of thinking net has to be strong, if your unfortunate enough to get it snagged it's better if it's weak enough to break with your pulling and then all you will have to do is maybe repair the odd mesh where it broke on retrieval, if it's too strong you may not be able to retrieve it if you can't break it free, it only needs to be strong enough to hold fish which weigh nothing while still in the water, 6lb or thereabouts breaking strain is adequate, properly set it will weigh very little and be very compact. Anything catched in a net can be retrieved and eaten, poison is very indiscriminate and kills everything and many dead fish are not retrieved and just lie dead rotting on the bottom, i would never use poison as i have seen poisoned rivers and the devastation is heart breaking and what eats the poisoned fish may also be poisoned, baits rely on fish feeding which if they are is fine, spearing is quite an acquired skill but works though you may go hungry in acquiring the skill needed if you don't have it. Used correctly in a survival situation you will not decimate the fish population as you will retrieve your net when your needs are fulfilled and all it catches can be eaten, and when you get out of there no trace will be left and no pollution left behind.